PLTDEV IN TRYING A FLT CONTINUATION WITH A PRIMARY ELECTRICAL PWR SUPPLY PROB.

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ON JAN/THU/97 AT APPROX AM00; I DEPARTED NEW ON A VFR FLT. THE FLT WAS ROUTINE ON CLBOUT; AND I SOON FOUND MYSELF OVER A 2500 FT CLOUD DECK. SHORTLY AFTERWARD; MY ALTERNATOR LIGHT CAME ON. I THEN WENT THROUGH A SERIES OF CHKS AND DETERMINED THAT THE ALTERNATOR WAS NOT PRODUCING PWR AND I WAS LOSING BATTERY PWR. AT THAT POINT I SHUT DOWN THE ALTERNATOR AND MASTER SWITCH AS A SAFETY PRECAUTION AGAINST POSSIBLE FIRE AND TO PRESERVE BATTERY PWR FOR LNDG. I CLBED TO 7500 FT TO LOOK FOR A BREAK IN THE CLOUD DECK BELOW TO ALLOW ME TO DSND FOR LNDG AT AN ARPT. I NAVED WITH A HAND-HELD GPS ALONG V198 WHILE AVOIDING CLASS C AND CLASS D AIRSPACE BELOW; LOOKING FOR A BREAK IN THE CLOUD DECK BELOW. AFTER 2 HRS; AND PAST THE MAI VOR; I TURNED AROUND AND HEADED BACK TO NEW WHICH WAS FORECAST CLR. AT ABOUT 30 MI OUT I CONTACTED NEW APCH CTL USING BATTERY PWR AND LOWERED THE LNDG GEAR. I WAS UNABLE TO MAINTAIN XPONDER AND RADIO OP DURING THE VFR FLT BECAUSE THIS WOULD HAVE DRAINED THE BATTERY LEAVING ME WITH NO ELECTRICAL PWR. UPON LNDG; THE ALTERNATOR WAS CHKED AT AN FBO AND FOUND TO BE BURNED UP AND TOTALLY INOP. IT WAS THEN REPLACED.